Grid bias regulator



Oct. 28, 1958 W B, BRUENE 2,858,454

n GRID BIAS REGULATOR Filed June 15, 1953 I A 2 Sheets-Sheet l Oar/D07 R JNVENTOR.

oct. 2s, 195s w. B. BRUENE 2,858,454

GRID BIAS REGULATOR Filed June l5, 1953 2 Sheets-Sheet 2 fu@ f /47 fawn/[r United States Patent() GRID BIAS REGULATOR Warren B. B ruene, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application June 15, 1953, Serial No. 361,804

9 Claims. (Cl. 307-44) This invention relates generally to grid bias regulators and relates particularly to a grid bias regulator which maintains electron tube quiescent plate current unaiected by disturbances which occur in either the plate voltage supply or the bias voltage supply.

A grid controlled vacuum tube produces a power output by the alternating component of its plate current through a load impedance. The ideal wave form ofthe alternating component of plate current is identical with the wave form of a signal voltage impressed on the grid of the tube. The signal output must not be alected by stray alternating voltage components from sources other than the signal voltage.

Vacuum tube operation requires constant direct voltage supplies for plate and grid. Any alternating components in the plate and grid supply voltages will cause distortion of the alternating plate current unless compensated. It is therefore an object of this invention to-nullify the eiect of variations in the plate and grid supply voltages upon signal output.

The ideal grid supply voltage has a zero impedance as well as a specied constant direct voltage. Very low impedance is particularly necessary where a signal causes grid current flow, which often occurs in power amplifiers. A ilow of varying grid current through the bias source impedance causes an alternating voltage component to be superimposed on the otherwise constant bias voltage and causes distortion in the signal output. Also, the direct voltage component of grid current alters the direct current bias voltage which further alters the operating conditions. It is therefore another object of this invention to provide a grid bias voltage source which presents virtually zero effective impedance to grid current flow.

The conventional grid bias supply attempts to approximate the ideal constant grid bias voltage andzero impedance. However its impedance is often variable with frequency and usually becomes large at frequencies near zero. The conventional type of bias supply is therefore unable to prevent distortion at sub-audio signal fre quencies. This portion of the frequency range is particularly important in single sideband transmission. It is therefore still another object of this invention to provide a virtually zero effective bias supply impedance to frequencies which approach zero. v

This invention differs from conventional voltage regulators in that it does not use a constant voltage as a reference, but instead uses the plate supply voltage as a reference. This invention acts to regulateathe ratio of grid to plate direct current supply voltages, and may be used with either class A, B or C operated tubes. Disturbances in the plate voltage, as for example, ripple, are compensated by a neutralizing opposing grid voltage which is generated by this invention.- Disturbances in the bias voltage, such as grid current flow through the bias source impedance for example, are also compensated by a neutralizing opposing grid voltage which is likewise generated by this invention. It is therefore yet another object ice of this invention to provide a bias regulator which maintains the signal output of an electron tube unaffected by fluctuations in either plate supply voltage or grid bias voltage.

This invention consists of a triode which has a grounded cathode connected serially to a resistor, and both are in series with a rectiiier bias supply circuit. A voltage dropping circuit is provided between the resistors ungrounded terminal and the local plate supply voltage, and a tap is taken from the dropping circuit through a direct voltage ampliiier to the control grid of the triode.

Further advantages, objects and features of this invention will be apparent to a person skilled in the art upon a further study of the specification and drawings, in which:

Figure 1 is a partial block diagram of this invention;

Figure 2 is a schematic diagram of one embodiment of this invention;

Figure 3 is a schematic diagram of another embodiment of this invention;

Figure 4 is a schematic diagram of still another embodiment of this invention; and,

Figure 5 is a graph which shows the voltage relationships in this invention.

The broader aspects of this invention are iirst considered in Figure l which shows the invention in partial block form connected to both a conventional power amplifier and a conventional plate voltage source which produces a voltage designated as B plus. A conventional power supply 10 is connected to an alternating current power source such as a common 115 volt source. The positive output terminal of rectifier 10 is connected to the plate of a triode or control tube 11 which has a grounded cathode. A resistor 12 has one end connected to the grounded cathode of tube 11 and its opposite end connectedto the negative terminal of power supply 10. The control grid 31 of tube 11 is connected through a direct current amplier 13 to an intermediate point on a voltage dropping circuit 14 which has one side connected to the ungrounded end of resistor 12 and its opposite side connected to a plate supply voltage 15.

Tube is a conventional power amplier which has a control grid 101 connected through a grid tank circuit 102 to the ungrounded end of resistor 12 which provides the inventions output bias voltage designated as C minus. An amplied signal voltage is provided to tank circuit 102 through the primary 106 of a transformer 104 which has a secondary 103 in tank circuit 102. Tube 100 is loaded by a plate tank circuit 107 which is connected to plate supply voltage 15. The output from tube 100 is taken from the plate and is furnished to a load through an impedance matching transformer 108.

The invention will now be considered in more detail from the embodiments shown in Figures 2, 3 and 4. Power supply 10 in Figures 2, 3 and 4 consists of a power transformer 17 which has: A primary coi] 16 connected to an alternating current power source, a secondary coil 18 with opposite terminals connected to respective plates of a double diode 23, and a filament coil 19 connected across the cathode lament of diode 23. A center tap 22 of coil 18 is connected to one side of a choke coil 24 which is in series with another choke coil 26 that has its opposite side connected to the ungroundedV end of resistor 12. A center tap 21 of coil 19 is connected to the plate 20 of tube 11. A capacitor 27 has one side connected to center tap 21 and its other side connected between choke coils 24 and 26. A second capacitor 28 has one side connected to center tap 21 and its other side connected to the ungrounded end of resistor 12.

Voltage dropping circuit 14 in Figure 2 consists of a voltage divider 33 which has one side connected to the ungrounded end of resistor 12 and its opposite side l? connected to the plate supply 15. A tap 32 of divider 33 is connected to grid 31 of tube 11. Tube 11 may act as an amplifier in Figure 2 since amplification occurs through the transconductance of tube 11.

Figure 3 shows another embodiment of this invention which differs from the embodiment of Figure 2 in -that instead of relying lon the amplification yof -tube 11,the separate direct current amplifier 13 has been added. -Rectifier 10, tube 11, resistor 12 and voltage dropping'eircuit 14 are identical with Figure 2. Direct current amplifier 13 includes a triode 40 which has: A cathode 42 connected to tap 32, a grounded grid 41, and a plate 43 connected to the B plus supply voltage through a resistor 44. The anode of a gas diode voltage regulator 46 Iis connected to plate 43 of tube 4h, and the cathode of gas diode 46 is connected to grid 31 of tube 11 and to the ungrounded end of resistor 12 through a resistor 47.

The embodiment shown in Figure 4 likewise differs from the embodiment of Figure 2 only in a portion of its detailed circuitry. Rectifier 1t), tube 11, and resistor 12 are identical with Figure 2. Divider 33 in dropping circuit 14 is connected between the B plus supply voltage and the anode of a voltage regulator tube 34 which has its cathode connected to the ungrounded end of the resistor 12. Tap 32 is connected to the cathode 53 of a tetrode tube 50 which has a grounded screen grid 51 and a plate 52 connected to the B plus supply voltage through a resistor 54. The control grid 56 is connected to the cathode of a voltage regulator tube 57 which has its anode grounded. A resistor 58 has one terminal connected to the cathode of tube S7 and its remaining terminal connected to the ungrounded end of resistor 12. Plate 52 of tube 50 is connected to control grid 31 of tube 11.

The basic operation of the embodiments shown in Figures l, 2, 3 and 4 is essentially similar and may be explained by the use of Figures l and 2, with later'reference to the embodiments shown in Figures 3 and 4.

It is readily noted in Figures l and 2 that the C minus bias voltage is the voltage drop across resistor 12 which is a function of the current through resistor 12 which is controlled by the grid Voltage on tube 11 and therefore the voltage at tap 32. A desired steady state C minus voltage is obtained by adjusting tap 32 to the desired grid voltage. The correct bias voltage may thus be obtained for amplifier tube 161i, and it is assumed a proper B plus voltage is obtained from source 15.

Let us first assume a disturbance in plate supply voltage source 15 which increases the B plus voltage on amplifier 100 above its desired value. The voltage kat the B plus end of divider 33 then rises and causes an decreases opposingly to maintain its normal value un- 'n affected by the change in plate voltage since the adjustment occurred instantaneously.

In like manner, a negative disturbance in plate supply voltage 15 will have substantially no effect on plate current, and likewise alternate positive and negative voltage disturbances, such as ripple, will not affect plate current. Line 60 in Figure 5 shows graphically the variation of C minus bias voltage with B plus plate voltage.

This invention also compensates for disturbances in the grid supply voltage. An example of a grid bias disturbance is the voltage generated by the flow of grid current through the bias source impedance. Grid current flow through resistor 12 has the effect of making the bias voltage more negative. instantaneously, the voltage at tap 32 and grid 31 decreases to decrease the current through tube 11 and resistor 12, which thereby opposingly makes the bias voltage more positive in an amount which instantaneously maintains the desired bias voltage and therefore the plate current at normal value.

In like manner, a positive disturbance in the bias supply a causes the voltage at tap 32 to increase which maintains -the C minus voltage and therefore the plate current normal. Thus, any disturbance in either the plate voltage supply or the grid voltage supply does not affect the plate current of a tube connected to the voltage supplies.

Changes in the direct current voltage at tap 32 are amplified by tube 11 and therefore have an increased effect on current in the rectifier circuit. The amount of amplification determines the ratio of the change of C minus voltage to the change of B plus voltage and is signified in Figure 5 by the slope of line 60. Sometimes various types of amplifier tubes 10i) make it necessary to obtain more amplification than can be obtained by tube 11. It then becomes necessary to provide further amplification such as shown in Figures 3 and 4. The slope of line 60 in Figure 5 is then increased.

Let us assume in Figure 3 that the B plus voltage is undesirably increased. The voltage at tap 32 then instantaneously increases to decrease the relative voltage between grounded grid 41 and cathode 42 which decreases the plate current of tube 40 that ows through resistor 44, and the voltage on plate 43 increases to increase the voltage on grid 31 of tube 11 through the constant voltage across tube 46. Gas Adiode 46 merely maintains the voltage on grid 31 at the proper voltage level since the plate voltage of tube 4t) ordinarily be too high. The resistor 47 is merely a load resistor for gas diode 46. Two stage amplification is therefore obtained for variations-in the direct voltage level at tap 32 through tubes 40 and 11.

The embodiment of Figure 4 obtains still further direct voltage gain. The Voltage across voltage regulator tube 34 is always constant. Therefore a variation in either B plus voltage or C minus voltage must occur across divider 33 because of the smaller voltage drop across divider 33; and the voltage variation at tap 32 is correspondingly greater. Tetrode S0 and resistor 54 operate substantially the same as triode 43 and resistor 44, however, tetrode 50 has greater gainthan triode 40. Grid 56 is maintained at a constant voltage level below ground by the constant negative voltage drop across gas diode 57. Resistor 58 is merely a voltage dropping resistor for gas diode 57. Since the voltage level on grid S6 is at a low level, the plate voltage of tube 50 is now at the proper level to drive directly grid 31 of tube 11.

The voltage ruglator circuit of this invention will therefore compensate for any voltage variations in a plate voltage source or a bias voltage source without distortion.

Although this invention has been illustrated by specific examples, it will be obvious to those skilled in the art that modifications may be made without departing from the scope of this invention.

I claim:

l. A source of grid bias supply voltage interlocked to a plate supply voltage for operating electron tubes free from disturbances in either supply source comprising, an independent source .of direct voltage, a resistor connected serially with said source, an electron tube having at least one grid, said electron tube connected serially with said source and said resistor, said resistor grounded at a point more positive than its negative terminal, a voltage divider connected at one end to the plate supply voltage and at the other end to the negative side of said resistor, means connecting an intermediate point of said divider to the grid of said electron tube, whereby said bias supply is provided from the negative side of said resistor.

2. Means for providing a grid bias supply voltage interlocked to a plate supply voltage to maintain the plate current of a connected amplifier free from disturbances in either of said Voltage supplies comprising, an independent source of direct voltage, a resistor connected serially with said source, an electron tube having at least one grid, said electron tube connected serially with said source and said resistor, said-resistor grounded at a point more positive than its negative terminal, a voltage dropping circuit asas,

connected on one side tol said plate voltage supply and connected on the other side to the negative end of said resistor, and a direct current amplilier connected at its input side to an intermediate point on said voltage dropping circuit and connected at its output side to the grid of said electron tube, whereby the negative grid bias supply Voltage removed from the negative end of said resistor.

3. An interlocked voltage bias supply comprising, an `alternating current power source, a rectiier power supply connected to said alternating current source, an electron tube with its plate connected to one side of said rectified power supply, the cathode of said tube connected to ground, a resistor connected between the cathode of said tube and the other side of said rectifier, a direct current amplifier with its output connected to the control grid of said electron tube, a voltage dropping circuit with an intermediate point connected to the input of said direct current amplifier, said voltage dropping circuit connected on one side to the negative end of said resistor, a plate supply Voltage connected to the otherside of said Voltage dropping circuit, and the bias voltage removed from the negative end of said resistor.

4. An interlocked bias voltage supply comprising, a rectified power supply, a control tube with its plate connected to the positive side of said rectiier and its cathode connected to ground, a resistor connected between the cathode of said control tube and the negative side of said rectiiier power supply, a potentiometer with its variable contact connected to the grid of said control tube, one side of 4said potentiometer connected to the negative side of said resistor, a plate voltage supply connected to the other side of said potentiometer, and the bias supply removed from said resistor.

5. A regulated bias voltage supply for maintaining within a connected electron tube a substantially constant ratio of direct plate voltage to grid Voltage comprising, an alternating current power input, means for rectifying said alternating input, a control tube connected in series with the output of said rectifying means, a resistor connected in series with said control tube and the output of said rectifying means, said resistor grounded at its most positive end, a potentiometer with its variable contact connected to the input of said control tube, one side of said potentiometer connected to the negative end of said resistor, the plate supply voltage connected to the other side of said potentiometer, and said bias supply removed from said resistor.

6. A grid voltage supply arranged for maintaining within a connected electron tube a constant ratio of plate voltage to grid bias voltage comprising, an alternating current power input, means for rectifying said alternating input, a control tube with its plate connected to the positive output of said rectiying means and its cathode connected to gound, a resistor connected between the negative output of said rectiiying means and the cathode of said control tube, a direct current amplifier with its output connected to the control grid of said control tube, a potentiometer with its variable contact connected to the input of said direct current ampliiier, one side of said potentiometer connected to the negative end of said resistor, a plate voltage supply connected to the other side of said potentiometer, and said bias voltage removed from said resistor.

7. A bias Voltage supply for maintaining substantially constant the ratio of grid voltage to plate supply Voltage of an operably connected electron device comprising, an alternating current power source, means for rectifying the alternating current to provide a smooth direct current output, a control tube having at least one grid and connected in series with the output of said rectifying means, a first resistor connected in series with the output of said rectifying means and said control tube, said resistor grounded at its most positive end, a gas tube with its cathode vconnected to the grid of said control tube, a second resistor connected between the cathode of said lgas tube and the negative side of said first resistor, a voltage divider connected between the negative side of said iirst resistor and the plate supply voltage, a second electron tube with a grounded grid, a third resistor connected serially with said second tube in a circuit connected on one side to the plate supply voltage and connected on the other side to an intermediate point on said divider, the plate of said gas tube connected to said third resistor, and the bias voltrernoved from said first resistor.

8. A bias voltage supply for maintaining a predetermined ratio of grid to plate supply voltages comprising, an independent source of direct voltage, a control tube connected serially with said independent source, a resistor connected serially with said independent source and said ycontrol tube, said resistor grounded at its most positive end, a direct current amplifier with its output connected to the control grid of said control tube, a voltage divider circuit comprising, a gas tube and a potentiometer connected in series between Said plate supply voltage and the negative side of said resistor, with the variable contact of said potentiometer connected to the input of the direct current amplifier, and said bias voltage removed from said resistor.

9. A voltage regulator for maintaining a predetermined ratio of grid to plate supply voltages comprising, an alternating current power source, means for rectifying said alternating power, a control tube connected serially with the output of said rectifying means, a first resistor connected serially with said rectiiied output and said control tube, said resistor grounded at its most positive point, a potentiometer, a gas tube connected serially with said potentiometer in a circuit that is connected on one side to the plate supply voltage and on the other side to said iirst resistor, a second electron tube having a plurality of grids with one of said grids connected to ground, a second resistor connected serially with said second tube in a circuit connected at one end to the plate supply voltage and connected at the other end to the variable tap of said potentiometer, the grid of said control tube connected to a point intermediate said second resistor and said second tube, a second gas tube, a third resistor connected serially with said second gas tube to comprise a circuit connected to ground at one end and to the first resistor at the other end, a second grid of said second electron tube connected to an intermediate point between said second gas tube and said third resistor, whereby the bias voltage is removed from said iirst resistor.

References Cited in the file of this patent UNlTED STATES PATENTS 2,102,779 Beers Dec. 21, 1937 2,243,442 Schade May 27, 1941 2,361,889 Walsh Oct. 31, 1944 2,431,306 Chatterjea et al, Nov. 25, 1947 2,434,939 Levy Ian. 27, 1948 2,480,418 Paradise et al Aug. 30, 1949 2,504,480 Wippert Apr. 18, 1950 2,696,587 Stratton Dec. 7, 1954 FOREIGN PATENTS 705,477 Germany Apr. 29, 1941 

